Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.4.21.5 (thrombin)
33,306 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The activities of adenylate and guanylate cyclase and cyclic nucleotide 3':5'-phosphodiesterase were determined during the aggregation of human blood platelets with thrombin, ADP, arachidonic acid and epinephrine. The activity of guanylate cyclase is altered to a much larger degree than adenylate cyclase, while cyclic nucleotide phosphodiesterease activity remains unchanged. During the early phases of thrombin-and ADP-induced platelet aggregation a marked activation of the guanylate cyclase occurs whereas aggregation induced by arachidonic acid or epinephrine results in a rapid diminution of this activity. In all four cases, the adenylate cyclase activity is only slightly decreased when examined under identical conditions. Platelet aggregation induced by a wide variety of aggregating agents including collagen and platelet isoantibodies results in the "release" of only small amounts (1-3%) of guanylate cyclase and cyclic nucleotide phosphodiesterase and no adenylate cyclase. The guanylate cyclase and cyclic nucleotide phosphodiesterase activities are associated almost entirely with the soluble cytoplasmic fraction of the platelet, while the adenylate cyclase if found exclusively in a membrane bound form. ADP and epinephrine moderately inhibit guanylate and adenylate cyclase in subcellular preparations, while arachidonic and other unsaturated fatty acids moderately stimulate (2-4-fold) the former. It is concluded that (1) the activity of platelet guanylate cyclase during aggregation depends on the nature and mode of action of the inducing agent, (2) the activity of the membrnae adenylate cyclase during aggregation is independent of the aggregating agent and is associated with a reduction of activity and (3) cyclic nucleotide phosphodiesterase remains unchanged during the process of platelet aggregation and release. Furthermore, these observations suggest a role for unsaturated fatty acids in the control of intracellular cyclic GMP levels.
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PMID:Cyclic nucleotides and platelet aggregation. Effect of aggregating agents on the activity of cyclic nucleotide-metabolizing enzymes. 0 49

The in vitro effects of N-3-(1-benzyl-cycloheptyloxy)-propyl-N,N-dimethylammonium-hydrogenfumarate (bencyclan) on clotting, fibrinolytic and platelet function test were investigated by adding the drug to normal human plasma. An anticoagulant activity, mainly of an antithromboplastin nature (directed against later stages of intrinsic thromboplastin formation and against tissue thromboplastin), was observed, while thrombin phase was unaffected. No effect was found in the fibrinolytic system tested (euglobulin lysis, UK-activated fibrinolysis, "hanging clot" method). The drug, although capable of aggregating platelets by itself at very high concentrations, showed a striking inhibitory effect, over a wide range of concentrations, both on platelet aggregation induced by ADP, epinephrine or collagen and on platelet adhesiveness to glass or collagen. Clot retraction was also clearly inhibited. PF3 availability was influenced with a peculiar two-phase behaviour dose-dependently. High concentrations showed a promoting action, while the lower were obviously inhibitory. It is suggested that the effects on platelet function may be due to an influence of the drug on cell membrane.
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PMID:In vitro effects of bencyclan on coagulation, fibrinolysis and platelet function. 1 70

Noncovalently bound fluorescent probes have been used to study changes in the platelet which may occur during platelet aggregation. Platelets were exposed to either N-phenyl-naphthylamine (NPN) or 8-anilino-1-naphthalene-sulfonic acid (ANS). Both dyes were bound by the platelet, and platelet aggregation by collagen or thrombin was unaffected by the presence of the label. No change in fluorescence intensity or wavelength of maximum intensity was observed during platelet aggregation.
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PMID:Fluorescent labeling of human platelets. 5 54

Platelet and fibrinogen survival and turnover studies have shown that platelet activation and fibrin formation may occur to different degrees in different thrombotic disorders. More direct evidence of differential involvement of platelet activation and fibrin formation should be provided by specifically measuring the products of these reactions, i.e. released platelet proteins and fibrinopeptide A. Two platelet proteins, platelet factor 4 (PF4) and beta-thromboglobulin (betaTG), were isolated and characterized, and sensitive and specific radioimmunoassays were developed to measure them. These assays were employed, along with the radioimmunoassay for fibrinopeptide A (FPA), to study the release of PF4 and betaTG in relation to FPA cleavage. PF4 and betaTG were released by ADP and collagen with time course and concentration dependence similar to that of [14C]serotonin release. FPA was not cleaved from fibrinogen during ADP or collagen-induced platelet release. Thrombin caused release of PF4 and betaTG as well as cleavage of FPA. Cleavage of FPA occurred with concentrations of thrombin about 100 times less than did release of PF4 and betaTG, and release of [14C]serotinin required still higher thrombin concentrations. Release of [14C]serotonin and platelet proteins was similar as a function of time. Sodium citrate was found to inhibit platelet release induced by thrombin.
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PMID:Radioimmunoassay of platelet factor 4 and beta-thromboglobulin: development and application to studies of platelet release in relation to fibrinopeptide A generation. 7 21

In thrombin-induced DIC, acetylsalicylic acid (ASA) prevents the strong initial fall in platelet count and the obturation of the microvasculature of the lung with platelet aggregates. During the DIC reaction increasing inhibition of aggregability of circulating platelets against collagen and ADP is observed. Furthermore, ASA prevents the increase in the plasma haemoglobin level caused by DIC.
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PMID:[Effect of ASS on platelet function in experimental DIC]. 9 74

Quantitative studies were carried out of the in vitro and ex vivo effects of phenylbutazone and 3-oxoalkyl substituted diphenyldioxopyrazolidines (kebuzone, tribuzone, benzopyrazone) on platelet aggregation. The specified pyrazolidine derivatives exhibited in vitro inhibitory effects on secondary platelet aggregation (induced by adrenaline and collagen), commensurable with the effects of sulfinpyrazone. The ex vivo efficacy was markedly influenced by the height of the drug level in blood and by differences in the elimination kinetics of the pyrazolidine derivatives in human organism. Inhibitory activities against primary aggregation (induced by ADP and thrombin) were found in vitro mainly in the phenyloxoalkyl derivative of diphenyldioxopyrazolidine (benzopyrazone) and its analogues. By substitution on the phenyl attached to its alkyl side chain (for example, by a halogen in the meta position), compounds were obtained which also possessed higher activities inhibiting secondary platelet aggregation.
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PMID:Pyrazolidine derivatives: a comparative study of their effects on platelet aggregation. 9 76

Salicylic acid, 1,10- and 1,7-phenanthroline prevented inhibition by aspirin of platelet aggregation and of generation of thromboxane A2 due to arachidonic acid, to the ionophore A21387, to thrombin and to collagen. Dithiothreitol, another drug which prevents aggregation and formation of thromboxane A2, but only reversibly, failed to interfere with the inhibition by aspirin. Irreversible inhibition by indomethacin and by the substrate analogue 5,8,11,14-tetraynoic acid was also unaffected by salicylic acid or by 1,10-phenanthroline, which thus probably exert a specific interaction with the aspirin-binding site. Inactivation of platelet cyclo-oxygenase with arachidonic acid led to inhibition of the formation of thromboxane A2 and of aggregation due to arachidonic acid itself and to collagen, but barely affected aggregation by thrombin, even though generation of thromboxane A2 was blocked. Use of salicylic acid and of reversible inhibitors of cyclo-oxygenase may help to unravel the mechanism of inhibition due to other agents.
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PMID:The inhibition of cyclo-oxygenase of rabbit platelets by aspirin is prevented by salicylic acid and by phenanthrolines. 9 21

The presence of specific Factor VIII/von Willebrand factor (FVIII/vWF) binding sites on human platelets has been demonstrated by using 125I-FVIII/vWF and washed human platelets. Binding is ristocetin-dependent and increases in proportion to the concentration of ristocetin from 0.2 to 1 mg/ml. Binding of 125I-FVIII/vWF to platelets can be competitively inhibited by unlabeled human or bovine FVIII/vWF, but not by human thrombin, fibrinogen, alpha 2-macroglobulin, equine collagen, or a lectin of Ricinus communis. Scatchard analysis of binding data indicated that the dissociation constant of FVIII/vWF receptors is 0.45--0.5 nM. There are 31,000 binding sites per platelet at 1 mg/ml of ristocetin concentration. The optimal pH range for binding is from 7.0 to 7.5. At a concentration of 2 mM, EGTA inhibits 86% of the binding; however, 20 mM of Ca++, Mg++, or EDTA have little effect. Binding sites for FVIII/vWF were found only on platelets, and no significant binding was detected with human erythrocytes or polymorphonuclear leukocytes.
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PMID:Demonstration and characterization of specific binding sites for factor VIII/von Willebrand factor on human platelets. 10 91

alpha(2)-Plasmin inhibitor (alpha(2)PI) is a recently characterized, fast-reacting plasmin inhibitor in human plasma that appears to play an important role in regulation of in vivo fibrinolysis. We report here a case of complete deficiency of alpha(2)PI in man. The patient, a 25-yr-old Japanese man, had a life-long severe bleeding tendency (hemarthrosis and excessive bleeding after trauma). The following tests were within normal limits: platelet count, bleeding time, thrombin time, prothrombin time, partial thromboplastin time, titers of known clotting factors, platelet glass bead retention, Factor VIII-related antigen, platelet aggregation by ADP, collagen and ristocetin, and clot retraction. Routine liver function tests were also normal. The only abnormal finding was that whole blood clot lysis was extemely rapid and was complete in 4-8 h. The concentration of plasma protease inhibitors, including alpha(2)-macro-globulin, antithrombin III, alpha(1)-antitrypsin, and C1INH, were all normal. The concentration of alpha(2)-PI in the patient's plasma, assayed by immunological methods, was <0.1 mg/100 ml (normal concentration, 6.1+/-0.88 mg/100 ml [mean+/-SE]) and functional assays showed a complete deficiency of alpha(2)PI. Addition of purified alpha(2)PI to the patient's whole blood completely corrected the accelerated fibrinolysis. The patient's parents, four siblings, and four other members of this family were asymptomatic, but the titers of alpha(2)PI in their plasmas were congruent with50% of normal pooled plasma. There were three consanguineous marriages in this family, and the alpha(2)PI deficiency appears to have been inherited as an autosomal recessive trait. We speculate that alpha(2)PI deficiency in this patient has led to uninhibited in vivo fibrinolysis that probably causes the severe hemorrhagic tendency. Thus, this study indicates the important role of alpha(2)PI in hemostasis.
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PMID:Congenital deficiency of alpha 2-plasmin inhibitor associated with severe hemorrhagic tendency. 15 96

Prostaglandin endoperoxides produced during aggregation of blood platelets are potent promoters of platelet aggregation and the release reaction. The present investigation has studied the effects of prostaglandin endoperoxides produced by platelet microsomes after incubation with arachidonic acid on the ultrastructure of platelets. Prostaglandin endoperoxides caused platelet pseudopod formation and internal transformation associated with a contractile wave within the platelet. The contractile process was similar to that seen following incubation of platelets with collagen or thrombin but was more complete than that seen with 25 muM ADP. Platelet aggregation was more prominent in unstirred samples incubated with the prostaglandin endoperoxides than in samples similarly incubated with 25 muM ADP. Dilatation of the open canalicular system was not a prominent feature except at 45 minutes after addition of the endoperoxides to the platelets, when the platelets appeared to be in a recovery phase. We conclude that the endoperoxides promote platelet stickiness and platelet aggregation by directly or indirectly stimulating the platelet contractile system.
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PMID:The influence of prostaglandin endoperoxides on platelet ultrastructure. 16 97


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